chemistry
posted by matt .
Sulphuryl chloride, SO2Cl2, decomposes according to the following firstorder reaction:
SO2Cl2(g) ¨ SO2(g) + Cl2(g)
At a certain temperature, it is observed that it takes 147 minutes for 23.0% of the sulphuryl chloride to react. Calculate the halflife for the reaction in units of min.

ln(No/N) = kt
Take No = 100, then N = 77, t is 147 min and solve for k.
Then k = 0.693/t_{1/2} and solve for t_{1/2}
Post your work if you get stuck. 
how did you get No and N?

I just assumed 100 for No (the number of molecules at the beginning), then if 23% react, that leaves 77. You could take ANY number for No and take 23% of that and subtract from No to obtain N. OR, you could take No = No, then N = 0.77*No but it's easier to stick in a number. Does that help.